Fix widgets not appearing after Homebrew upgrades

What's fixed

Widgets not showing up after upgrading via Homebrew. macOS keeps a registry of widget extensions, and stale entries from previous versions could block the current one from being discovered. The app now re-registers its widget extension on every launch, so widgets appear in the gallery regardless of how the app was installed or updated. Thanks @blackketter for the report (#218).
Deprecated NSApp.activate API replaced. Silences a deprecation warning on macOS Tahoe.
Launch diagnostics. The app now logs version, macOS version, and subsystem startup to the system log, making it easier to diagnose issues from Console.app.

brew upgrade --cask whatcable or download from Releases.